Pedal goes to the floor?

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g49bridges

g49bridges

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Hey guys, I'm not a brake guy so any advice would be great. I've got a 74 duster, and when you push the brake Pedro it goes to the floor. I've put on a new master cylinder, and new front calipers trying to fix this. I've bleed about a gallon of brake fluid through them too. Doesn't seem to push anymore air out, just fluid. With the car off you can pump them up a little and peddle will finally stop about 1 inch of the floor. But with it running and the booster helping it will go to the floor every time. I've jacked the front up and with the peddle flat on the floor the front brakes are working enough to hold the tires from turning, but only when it's flat on the floor. When driving it, it seems to only have rear brakes, and if you aren't careful you will lock up the rears. Like I said, I'm not really a brake guy, so any help here would be great.
 
Quick question: did you bench bleed the new master cylinder before install? I use the gravity bleeding method when I bleed my brakes ever since I put disc brakes on my 68 valiant because I tried pressure bleeding starting farthest from the MC first and when I would get to the front it was like there was nothing there.
 
did you mount the calipers on the correct side? (bleeder at top?) did you bench bleed master cylinder? are you bleeding starting at Pass. side front and working your way around to drivers front?
 
No I didn't bench bleed it. Pedal was doing the same thing with the old master cylinder, and found it was not putting pressure to the calipers, and was bypassing itself. So put on the new master cylinder, filled it full and started bleeding. Eventually it got to the point where it would pump up an inch of the floor. And that's after about 6 pumps. You can keep pumping the pedal all you want and it'll never stop any further from the floor.
 
You did not answer the question. If you have the calipers swapped side for side the bleeders will not be "at the top."

Also, what about rear shoe adjustment?
 
67Dart273 said:
You did not answer the question. If you have the calipers swapped side for side the bleeders will not be "at the top."

Also, what about rear shoe adjustment?
Click to expand...

X2, there was a similar problem not long ago on the board where a member didn't realize you couldn't bleed brakes if the bleeder wasn't at the top
 
67Dart273 said:
You did not answer the question. If you have the calipers swapped side for side the bleeders will not be "at the top."

Also, what about rear shoe adjustment?
Click to expand...

Yep, it will do that if the rears are out of adjustment because it takes the whole travel of the pedal to get the shoes out to the drum.
Also a clue that they are out of adjustment is that they lock up.
This happens due to a "camming in" of the shoes against the drum.
(means the shape of the shoe causes it to apply itself when the leading edge of the shoe touches the drum.)
 
Must have missed your post. Yes, bleeders are at the top. I've bleed both furthest to closest, and visa-versa...just trying different things so to speak. So let me get this straight...I have front brakes at the very bottom of peddle, but at that point the rears are locking up, so you are saying it could be the rears out of adjustment? I've pulled the e-brake(which functions like it should), and still have the same movement in peddle, if that matters.
 
How are you bleeding?

I like "old" methods. I don't believe in vacuum or gravity bleeding. I believe in keeping positive pressure "in" the system. This means pressure bleeding, or by 2 people "on the pedal."

Have someone pump it up. Release starting at furthest rear cylinder, a hose into a container. CLOSE the bleeder before the pressure falls off completely and do not allow your helper to release the pedal before you get the bleeder closed.

If worst comes to worst, read the shop manual on checking procedures, which give some pressure checks

Buy some plugs / unions. This will allow you to pull the rear line loose at the rear axle and plug it, and temporarily eliminate the rears.

Master MUST be bled at the master first.

It's possible that "half" the master is not working. Have someone work the pedal. You should see "action" as it returns in both halves of the master with the cap removed.
 
g49bridges said:
So let me get this straight...I have front brakes at the very bottom of peddle, but at that point the rears are locking up, so you are saying it could be the rears out of adjustment? I've pulled the e-brake(which functions like it should), and still have the same movement in peddle, if that matters.
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Yes that was the idea, but now that you said you pulled the ebrake and still apparently have the same pedal I have to agree with the bad or not bled master cylinder theory more.

I think Del is on to something with the "plugs" idea.
You could even check the master front and rear function by plugging one or the other of the ports.
 
You have air trapped in your master it sounds like to me. I had this happen once when my friend on my 3 man team doing the bleeding watched as the master cylinder went empty and the idiot had the following excuse "uh durrrr, I didn't know that it meant anything at all". after that, the brake pedal would go to the floor and I could get it to stop by pumping em.

Remove your master cylinder and use the provided plastic plugs that shoulda came with it. Be real gentle with em or they will strip right out. I did that myself, so learn from my mistake. handtight is alright here. Now, mount it up on a bench-vise and pump the center of the plunger where the pushrod would go with an adequate phillips screwdriver you don't care about (it'll get brake fluid on it and eat the paint off of it). Pump it AT MOST a 1.5" stroke until you see no more bubbles coming from the rear reservoir and see a slight disturbance in the tension of the brake fluid at the surface. Put the cap on the top and put the bail on it (the metal strap) and now mount it up in your vehicle and bleed from the furthest to closest to master cylinder
 
Don't forget to check the booster for vacuum leak's and the check valve for failure. And all your lines for breaks and leaks. Or it could be the booster it's self? But that usually causes hard brake peddle but you never know. Good luck someone here should be able to help figure it out!
 
g49bridges said:
Hey guys, I'm not a brake guy so any advice would be great. I've got a 74 duster, and when you push the brake Pedro it goes to the floor. I've put on a new master cylinder, and new front calipers trying to fix this. I've bleed about a gallon of brake fluid through them too. Doesn't seem to push anymore air out, just fluid. With the car off you can pump them up a little and peddle will finally stop about 1 inch of the floor. But with it running and the booster helping it will go to the floor every time. I've jacked the front up and with the peddle flat on the floor the front brakes are working enough to hold the tires from turning, but only when it's flat on the floor. When driving it, it seems to only have rear brakes, and if you aren't careful you will lock up the rears. Like I said, I'm not really a brake guy, so any help here would be great.
Click to expand...

Don't know if this will help, but 2 years ago I had the same issues,75 dart. The brake booster was bad. Didn't hear any vacuum leaks ect. I put all new pads/calipers/master cyl as I didn't feel comfortable with over 40 year old parts. Never thought of the brake booster causing issues. At first I had good brake pedal, for about a month then I had the same symptoms you describe. I went back through the system again and found nothing. Only thing I didn't replace was the booster. Purchased a remaned unit and turned in my old one for a core. Installed it and have had good brakes since. I figure the diaphragm probably had a small leak and wouldn't retain vacuum. Good luck..
 
:banghead:I wasted a huge amount of time when I had this problem, turns out I had the calipers reversed, I swore up and down that you could not reverse them, turns out you can't get all the air out if they are reversed. I stubbornly tried everything else first including bench bleeding the master cylinder, you should double check this simple item first.:banghead:
 
You don't need to remove the MC to "bench bleed" it. Indeed, I always do it on the car. You much bench bleed it, like >50 pumps to get all air bubbles out. Many videos on youtube.

If nothing else, suspect the booster as post #15 suggests. I would have sworn that a bad booster couldn't allow the pedal to sink, but several people said that changing the booster fixed that problem. Perhaps there are internal parts in the valve and force path that can fall out and allow more play.
 
BillGrissom said:
You don't need to remove the MC to "bench bleed" it. Indeed, I always do it on the car. You much bench bleed it, like >50 pumps to get all air bubbles out. Many videos on youtube.

If nothing else, suspect the booster as post #15 suggests. I would have sworn that a bad booster couldn't allow the pedal to sink, but several people said that changing the booster fixed that problem. Perhaps there are internal parts in the valve and force path that can fall out and allow more play.
Click to expand...

that is correct, bench bleeding is much easier on the car with the leverage of the brake pedal, and since its already mounted just unbolt the brake lines and install the bleeding plugs
 
A lot of good advice. Thanks guys. Had to leave the state for a few weeks on business, but as soon as I get back I will try bench bleeding the ms, double checking the calipers, and if that doesn't work it'll be time for a new booster. And if that still doesn't work I guess it'll have to sit until next spring when the whole car gets rebuilt including aftermarket brakes.
 
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